It is indeed a real shame that you missed the Global Continuous Casting Forum for copper practitioners which was held concurrently with Interwire 2011 May 01 through May 05 in Atlanta, Georgia. That was only four weeks ago. Perhaps somebody else from your company attended this Forum and brought back the literature that he/ she can share with you.

Anyway this Forum is far too limited to to discuss the issues that you are looking for. Instead think of the following sections:
Incorrect chemistry of the copper melt. (Purity, oxides, foreign materials.)
Incorrect casting. (Porosity)
Incorrect cooling.
Incorrect removal of the impurities after casting by scalping.
Incorrect rolling (Rolled in seams.)
Spalling from the rollers adding metal inclusions.
Pickling problems.

I'm sure you agree that tight management (process control) of all of the above are key for the production of quality copper rod.

Porosity is defined as a structure or part that is porous. (containing voids.)

Porosity may be a problem relating to the launder, the float control or the tundish itself. Contact the manufacturer of the casting machine for more information and trouble shooting if indeed you are getting porosity in the copper rod.

1) If the Hydrogen ppm is more in copper rod is that also one of the way to form porosity?
2) Why do we maintain the Oxygen ppm in copper rod? If oxygen is more or less in rod what are the problems that occur?

I see you know a lot more about the chemistry of copper then you previously let on. I am not a chemical engineer or a chemist so if you want a quick and very detailed answer, I suggest you contact your machine manufacturer. (Contirod, Southwire SCR or Continuus Properzi) You could also discuss this with a faculty member in the metallurgical engineering department of your local engineering university.

I will however try to give you some insight with my limited understanding of casting technology.

Oxygen and Quality
The oxygen content of the molten copper is usually checked in the launder and the tundish by some type of oxygen sensor. In normal operation, the molten copper exiting the shaft furnace has an oxygen content of 50 to 75 PPM. During transfer of the molten metal to the tundish, the oxygen content is raised to 250-350 PPM. This controlled addition of oxygen is important in minimizing the hydrogen content in the molten metal. Likewise many impurities are oxidized and precipitated out. This significantly reduces the effects of the impurities on resistivity. The oxygen content afterwards should be less than 200 to 350 PPM to stop significant formation of Cu2O along the dendritic boundaries. If the final oxygen content exceeds the upper limits of about 350 to 400 PPM, the higher amount of Cu2O can contribute to central burst failures at copper wire drawing. This however in my understanding does not contribute to porosity.

Temperature and Quality
The temperature of the molten copper must be carefully controlled to reduce the amount of dissolved hydrogen as the solubility of hydrogen increases with temperature. Thus the temperature of the molten copper must be maintained as low as practically possible. Too low a temperature however will make the molten metal too viscous and that will trap hydrogen or steam during solidification and that can result in porosity.